Several techniques have been employed in the art to attempt successful (reliable, substantially instantaneous) ignition of high voltage flashlamps. In those lamps mentioned above which include a glass bead with the lead-in wires embedded therein, a single, relatively large mass of primer material was positioned on the bead to bridge the two ends of the wires. Application of the aforementioned high voltage pulse across the ends of the wires projecting externally of the lamp's envelope resulted in a voltage breakdown of the mass when a certain voltage level was reached. The previously non-conductive mass thus became highly conductive and ignited to in turn ignite the shredded zirconium or hafnium combustible material located within the envelope relative to the primer mass and glass bead. A particular problem with this type of ignition was that it usually occurred at a localized point in the primer and was relatively slow in spreading to the remainder of the mass. This often resulted in unacceptable variations in ignition times. In addition, variations in thickness, homogeneity, or drying temperatures for such large masses of material also served to alter the range of ignition voltages required to effect successful lamp firing. In another type of technique for igniting a high voltage flashlamp, only one of lamp's lead-in wires was coated with a porous insulating material and both wires then bridged by primer. This ignition, often referred to as of the discharge variety, was achieved by impressing a pulse of more than 10,000 volts across the externally projecting wires. Spark discharges were produced across the porous insulator between the lead coated with the insulating material and the primer material to ignite the latter. One problem with this type of lamp was the difficulty incurred in attempting to fully cover the one wire with insulating material. Yet another problem was the inherent requirement for such high voltages essential to achieve ignition.
In yet another flashlamp (of the discharge ignition type), only one of the lead-in wires projecting within the envelope was coated with an insulating material which in turn also served as a primer. The lamp's shredded combustible provided a conducting path between the primer and adjacent, uncoated wire. Again, difficulties were experienced in such a lamp due to the extreme difficulty in fully coating the one wire. There is also an inherent problem in any lamp ignition system which relies on the shredded combustible filaments to form part of the circuit thereof. On many occasions, electrical interconnection was prevented as a result of a shifting or settling of combustible at spaced locations within the envelope. Alternatively, when contact was provided, it was impossible to ascertain the extent to which such contact was achieved (e.g., number of shreds providing the conductive path), thus resulting in unacceptable variations in conductivity between different lamps.
It is believed, therefore, that a high voltage flashlamp which is capable of providing substantially instantaneous and reliable ignition without the several disadvantages of many presently known lamps as described above would constitute a significant advancement in the art.